At the Farnborough Air Show in the UK, CFM International (CFM), a 50/50 joint venture between Snecma (SAFRAN Group) and General Electric Company, introduced LEAP-X (Leading-Edge Aviation Propulsion), an entirely new baseline turbofan engine for current narrow-body aircraft that offers up to a 16% reduction in fuel burn.

In parallel, the company is also working on an open rotor engine that would deliver even greater fuel efficiency benefits.

The first full LEAP-X demonstrator engine is scheduled to run in 2012, and LEAP-X could be certified by 2016. CFM says that the new turbofan will reduce the engine contribution to aircraft fuel burn by up to 16% compared to current CFM56 Tech Insertion engines that power Airbus A320 and Boeing Next-Generation 737 aircraft. Additional fuel burn improvements will be achieved once this engine is paired with new aircraft technology.

A large contributor to the increased fuel efficiency of the engine is an all-new composite fan blade produced with three-dimensional, woven resin transfer molding (3-DW RTM) technology that dramatically reduces engine weight while providing a more durable blade. The new composite technology enables a reduction in engine weight by approximately 400 pounds and in the fan blade count by 25% (from 24 to 18).

Development of ceramic matrix composite (CMC) technology has been underway at GE for more than 25 years. This ultra-light-weight material can support the extremely high temperatures found in the high-pressure turbine. Titanium-Aluminide (Ti-Aluminide), a lightweight alloy that has been under development for the past 20 years, will also be incorporated into the engine.

In late 2008, CFM will perform a series of full-scale fan demonstrator engine tests with the 3-DW RTM fan blades being developed as part of Snecma’s MASCOT program. The engine will complete performance ground tests at Snecma facilities in Villaroche, France, before being transported to GE’s outdoor test facility in Peebles, Ohio, for acoustic and crosswind testing.

The first full core is scheduled to begin testing next year. Hardware for the core, which features an eight-stage compressor (compared to nine in the current CFM56) and single-stage turbine, is being produced now and the core is targeted to fire by mid-2009. A second core test is also planned. The combustor is an advanced version of the TAPS design. (Earlier post.)

The GE36 unducted fan (open rotor). Click to enlarge. Source: GE

Open rotor. An open rotor engine is a modified turbofan, with the fan blades placed outside the engine nacelle. Last seriously explored in the 1980s, the open rotor prototypes (such as the GE36 from General Electric) delivered a 30%+ increase in fuel efficiency. Noise, vibration, size and maintenance were issues with the open rotor concepts at the time.

With current progress in modelling and design, however, air engine manufacturers are again looking at this approach. In May, Aviation Weekreported that GE and NASA were reviving studies of the abandoned GE36 unducted fan.

Under the cost-sharing Space Act deal with NASA, GE will refurbish all the original unducted fan (UDF) test rigs, and, with the agency, will begin a rigorous analysis of data collected during the $1.2-billion propfan program that ended almost 20 years ago. “We will then be looking at all the new technology that can be added to the system that ran back then, and at what the core would be like, the materials properties of the blades and the fan shapes,” according to GE.

The thrust of the open rotor study, which is still in the stages of being refined, is to overcome noise and mechanical complexity—two major hurdles that stymied the original propfan projects.

CFM is currently conducting studies in four areas for the open rotor configuration: fan aerodynamics and acoustics; mechanical design, including a pitch change mechanism; aircraft installation; and certification methodology. Technology demonstration tests begin next year and will extend through 2011.

When we launched the LEAP56 technology development program in 2005, fuel was at $1.30 a gallon. Today, airlines are paying nearly $4.00 a gallon. Our customers are hurting and we are responding. LEAP56 is the single largest investment in technology in our history; we are bringing the full technical and financial resources of our parent companies to bear to give them a solution: LEAP-X. We have set aggressive targets for this engine, and the technology plan is in place to achieve them.

We are excited about this new engine, but we also think we need to remain flexible. If fuel prices continue to rise, we will need to raise the bar even higher and introduce even more advanced technology. For the next three years, we are pursuing parallel paths: the LEAP-X advanced turbofan and the open rotor. The foundational technologies support either architecture, and we are making good progress toward finding solutions for the inherent technical challenges of an open rotor configuration.

It's truly a shame the UDF program was ever abandoned--a testimony, I would say, to the oil industry's ability to egg on our short-sighted side in politics. If it was alive and ready in our arsenal now, the airlines, and the free world in general, would be hurting far less today. Ditto with some other aeronautic efficiency programs, such as laminar flow control.

When GE was testing their UDF engines, it was on a sort of a hybrid aircraft--one UDF engine combined with some tried-and-true standard turbojets. They only had in mind testing for doing this, but they really should have gotten planes into production with both types of engines. It would have reduced all the new costs, (high at first on something radical like that), enabled it to be rolled out faster, kept safety high, and still would have given the bulk of the fuel-sipping benefit because you would basically run on that one engine in cruise. Noise doesn't matter at cruise altitude, making that issue easier. Active Noise Cancellation should fix the cabin noise from these.

BTW propfan was the term favored by competitor Pratt and Whitney. The new term Open Rotor says the marketing boys have been busy, which is a good sign because it suggests they really want to sell these engines.

Another thing that should be worked on is long-wing aircraft designed to save fuel by flying slower. More aircraft (product of the free world) in lieu of petroleum which is not.

With the price of fuel (fossil and/or bio) going up rapidly, higher efficiency turbo-prop planes find more and more takers. Active cabin noise concellation systems and better noise isolation materials can make turbo-prop planes almost as quiet as Jet units.

More operators are switching to higher capacity, higher efficiency, high speed Regional Turbo-prop aircraft to reduce their fuel bill.

I don't think there was a conspiracy back when the previous open rotor engine tech programs were abandoned. Oil/kerosene was cheap and the fuel efficiency benefit didn't justify the anticipated higher purchase cost, maintenance and other issues of existing turbofans (CFM56 and V2500) - at the time. Now with oil at $140 a barrel that's all changing, wait till we see oil at $300 a barrel... With two airframes already launched (Canada and Japan) with the Pratt Geared Turbofan - it'll be interesting to see if Airbus and Boeing will have to go for the Open Rotor config to get the extra efficiency and gain a sales edge (or risk ceding the 100-150 seat market to the previously launched aircraft).

Good evening,
I worked for McDonnell-Douglas in 1987 when the UDF/Propfan was a going concern. The project was abandoned because nobody wanted to pony up for the development cost. We had an MD80 derivative design that was slated for production in 1991 (you can see it in some of the Av Week and Commercial Aircraft compendiums of the day). It would have offered 60% less fuel consumption than contemporaries. In 1991 Kuwait was invaded, fuel costs went up 60% and all of a sudden anyone (who bothered to care) realized that we should have followed through with it.

There were plenty of other problems that haven't been mentioned here, including wing de-icing. As the lead engineer on our flight test training simulator project, I was aware of the disastrous calamities that could happen because I had to make sure we could train the pilots for them. However, if you look back at the colossal problems that had to be overcome by jets when they were first introduced the UDF was a piece of cake.

If corporations can look beyond the current quarter they'll go for radically more fuel efficient airframes. It was frustrating how long it took though. The first gas crisis occurred when I was learning to drive in 1973. It wasn't until I'd been out of college for 4 years that the airframers seriously started designing the propfan.

A number of small planes have been equipped with diesel engines that burn jet fuel and more are being built new. Is a diesel engine with prop more efficient than a fan-jet or even a turbo-prop. The compression ratio in large fan-jets is 30 to one, but a lot of energy is used to do the compression. Turbo-prop planes are known to be more efficient already and perhaps they should be required for all short flights where speed is not important. Perhaps jet-speed should be considered a luxury similar to driving a Hummer. Fuel-per-passenger mile performance of every airline and aircraft should be reported, but also the fuel use for transporting freight should be known and subtracted. Obviously there is a need for airline re-regulation. If they are all going broke when left to their own control. ..HG..